self:SetMaximumSize(500,1200) defines the largest size we want to allow the window to be resized to.

self:SetMinimumSize(300,1200) defines the smallest size we want to all the window to be resized to.

self:SetResizable(true) is where the magic is. This tells Lotro that the user should be able to resize the window. Mouse pointer will automatically change when positioned over the lower and right border of the window.

function ListWindow:SeizeChanged(args) is where we catch the rezising of the window. Here we need to reposition and resize all our child controls.

It is actually this easy to make a window resizable. The biggest part is the SizeChanged method where we need to resize and reposition our child controls.